1. Field of the Invention
This invention relates to a condenser installed in a power generating plant and the like for condensing steam turbine exhaust.
2. Description of the Related Art
FIG. 6 and FIG. 7 show a schematic constitution of a conventional condenser, indicating a front elevational view and a side view of the condenser respectively. The condenser includes a huge condenser shell 1 having an approximately square-shape, and a steam turbine 2 is placed on an upper portion of the condenser shell 1. A large number of condenser tubes are housed inside the condenser shell 1, composing a large tube bundle 3.
The tube bundle 3 is supported by a plurality of tube support plates 4 provided along a longitudinal direction of the condenser tube as shown in FIG. 7. Condenser tube plates 5 are provided vertically at both end portions of the condenser tubes, and condenser water boxes 6 are continuously provided at the condenser tube plates 5. Besides, an entrance/exit 7 and an entrance/exit 8 for a circulating medium (generally, circulating water such as seawater, water from a, cooling tower or the like is used) at the condenser tubes are provided to the condenser water boxes 6.
According to the condenser having the above-mentioned structure, steam flowing to the condenser shell 1 from the steam turbine 2 as shown by an arrow in FIG. 6 performs a heat exchange with the circulating water passing inside the condenser tube bundle 3 through the condenser water box 6. The steam lost its latent heat is condensed and gathered to a hot well 9 in a bottom of the condenser shell 1. The circulating water absorbing heat is discharged outside through the condenser water box 6 at the other end of the condenser tubes.
Since a concentration of noncondensing air included in the steam increases gradually when the steam is condensed gradually with its latent heat lost by the circulating water while passing through the tube bundle 3 as described above, the steam which has high noncondensing air concentration is led to an air cooling zone 10 and condensed further to increase the noncondensing air concentration as much as possible. After that, the steam is ejected outside the condenser through a noncondensing air ejection duct 11 by an air ejector (not shown).
Next, technical problems in terms of the condenser and the methods for solving the problems of the conventional condenser will be explained.
In the condenser, steam condensation progresses by a temperature difference between the steam and the circulating water. The temperature whereat the steam is condensed is a saturation temperature for a steam partial pressure in a condensation surface. However, the steam partial pressure is lowered broadly by two factors, and condensation performance (heat exchange efficiency) is lowered by accompanied decrease of the temperature difference. One factor is a pressure loss caused by steam flow, and the other factor is increase of noncondensing air partial pressure by the condensation of noncondensing air mixed in the steam.
Therefore, a reduction of the pressure loss and a prevention of noncondensing air retention are important for achieving performance improvement in the condenser.
In general, exhaust pressure of the steam turbine has relation to the pressure loss of the condenser and the noncondensing air concentration inside the condenser. The exhaust pressure of the steam turbine is a pressure calculated by adding the steam pressure loss in the condenser to a pressure whereat the steam is condensed in the condenser tube bundle. Therefore, when the steam pressure loss in the condenser is large, the exhaust pressure of the steam turbine is increased and a turbine output is lowered, as a result of which, power generating efficiency is reduced. Thus, to keep the steam pressure loss low in the condenser and to lead the steam to the air cooling zone smoothly without steam retention in the condenser tube bundle are important technical problems as performance indexes of the condenser.
In the conventional condenser, two different types of forms mainly respond to these problems. One of them is to provide a steam passage space wide enough around the condenser tube bundles arranged comparatively centered. (For example, refer to Japanese Patent Laid-open Application No. Hei 8-226776.)
The other form is to provide a steam passage wide enough in the tube bundles arranged sparsely as a whole in a wide range. (For example, refer to Japanese Patent Publication No. Sho. 55-36915.)
Demerits of the former of these types of forms are that the whole size of the condenser is enlarged by taking the surrounding steam passage space widely and that the pressure loss is comparatively large because the steam passes by a large number of condenser tubes until reaching the air cooling zone. The demerit of the latter is that a steam retention area in the tube bundle tends to be made because a path of the steam in the tube bundle toward the air cooling zone is complicated.
The above-mentioned condenser shown in FIG. 6 and FIG. 7 is a one-path type condenser in which the circulating water flows in from one condenser water box 6 and flows out to the other condenser water box 6, however, there exist in general a two-path type condenser in which one condenser water box has an entrance and an exit for the circulating water and the circulating water turns back at the other condenser water box.
FIG. 8 shows a sectional construction of one example of the two-path type condenser of which tube bundle is divided into upper and lower bundles. This condenser is so constructed that the circulating water flows in from an upper bundle 31 provided above and flows out from a lower bundle 32 provided below, or on the other hand, that the circulating water flows in from the lower bundle 32 and flows out from the upper bundle 31. In addition, the upper and lower bundles are partitioned by a partition plate 33. (For example, refer to Japanese Patent Application Laid-open No. 2001-153569.)
Since the outermost periphery length of the tube bundles is longer than the condenser having one tube bundle by dividing the bundle into two in such two-path type condenser, steam speed whereat the steam flows in the tube bundle is reduced. As a result, an effect that the pressure loss of the steam generated in the tube bundle is suppressed can be obtained. However, since the air cooling zone 10 and the noncondensing air ejection duct 11 are required to be provided at respective tube bundles by dividing the tube bundle into two, there exists disadvantages that a structure is complicated, and a manufacturing cost increases.